1. Field of the Invention
The present invention relates to ceramic and ceramic matrix composite (CMC) tile armor, and specifically to armor that has reinforcement of the joints and free edges of the armor with glass or ceramic strips. These strips, according to the invention, are applied over the ceramic armor joints and edges and thereby increase the armor's ability to withstand a variety of ballistic threats. The purpose of this invention is to provide optimal armor protection capability for ground vehicles, watercraft, aircraft, spacecraft and, in body armor applications, for personnel.
2. Background of the Invention
Lightweight, composite ceramic tile armor has proven an effective countermeasure against a variety of ballistic threats including lead core, steel core, armor-piercing rounds, and fragments. However, it is also known that the protective value of ceramic armor progressively degrades as impact points approach the edges, corners, and abutting joints between individual tiles. Typically, in the case of a 6 inch.times.6 inch tile, as much as 60 percent of the tile's area could provide substandard ballistic protection in comparison to protection afforded against impact at the tile's center. In a 12 inch.times.12 inch tile, as much as 30 percent of the tile's area could be substandard, and in the case of a 15 inch.times.15 inch tile, as much as 20 percent. As a consequence, larger tile configurations are being used as one method of reducing the joints areas and increasing the overall percentage of tile performing optimally in any given arrangement. Additionally, vulnerable joint and free-edge areas typically are cut, pressed, or ground at substantially greater thicknesses (an approach known as the "raised edge" enhancement) in an effort to counteract the inherently weaker performance characteristics of these areas.
These improvements, however, have limitations. Large individual tiles are not adaptable to as great an arrangement of surface configurations as are small tiles. Large tiles also exhibit a greater degree of crack propagation, particularly after multiple hits, than smaller tile segments which are separated within the seams of the abutting joints by adhesive or flexible rubber strips. As a result of this increased crack propagation, a greater percentage of the overall armor is therefore damaged than would be the case with smaller tiles. Raised-edge enhancements improve the tile's protective performance, but are more difficult and costly to manufacture than flat, constant-thickness tiles.
Three U.S. patents, described below, illustrate methods for providing improved free edge or joint protection without encountering the disadvantages associated with the use of large tile and raised-edge enhancements. U.S. Pat. No. 3,859,892 discloses ceramic composite tile armor having a free edge, in which improved performance against high-energy projectiles at the free edge is achieved if the glass laminate backing is folded over at an angle of substantially 90 degrees and bonded along the side of the exposed edge to create an enclosing lip or flange. In another embodiment disclosed in this patent, improved ballistic performance is achieved by folding back the laminate at an angle of substantially 180 degrees along the length of the edge and then bonding the laminate to itself. U.S. Pat. No. 3,592,942 discloses improved free-edge protection employing a similar method of folding at an angle of substantially 90 degrees to create an enclosing lip or flange, but describes aluminum alloy, rather than glass laminate, as the preferred backing material. Both these improvements, however, are limited solely to the protection of the free edges of ceramic composite tile armor. They cannot be applied to the similarly vulnerable corners and abutting joints between individual ceramic armor tiles. U.S. Pat. No. 3,683,828 discloses improved ballistic protection at the free edges and at the joints between ceramic composite tiles through the placement of carbon steel, alloy steels, or titanium strips directly under the free edges and joints. The metallic strips are set along the entire length of all free edges and joints, and bonded with an adhesive between the outer layer of ceramic tile and the underlying layers of laminate fibrous backing. This enhancement is effective in improving ballistic protection, but is both costly and difficult to manufacture. Furthermore, indentations precisely corresponding to the length, width, and thickness of the metallic strips must be made in the laminate fibrous backing before the strips themselves are applied and the ceramic tiles set and adhered over them. Once the ceramic tiles are in place, there is no cost-effective method to assure that the metallic strips remain placed as intended as the entire armor assembly is cured.